Volcano Contours Example
A colored contour plot of the Maungawhau volcano in New Zealand. This example demonstrates contour generation directly from a provided grid of data values, rather than performing kernel density estimation on a discrete point set.
Vega JSON Specification <>
{
"$schema": "https://vega.github.io/schema/vega/v5.json",
"description": "A contour plot of the Maungawhau volcano in New Zealand.",
"width": 960,
"autosize": "none",
"signals": [
{
"name": "grid",
"init": "data('volcano')[0]"
},
{
"name": "height",
"update": "round(grid.height * width / grid.width)"
},
{
"name": "smooth", "value": true,
"bind": {"input": "radio", "options": [true, false]}
}
],
"data": [
{
"name": "volcano",
"url": "data/volcano.json"
},
{
"name": "contours",
"source": "volcano",
"transform": [
{
"type": "isocontour",
"scale": {"expr": "width / datum.width"},
"smooth": {"signal": "smooth"},
"thresholds": {"signal": "sequence(90, 195, 5)"}
}
]
}
],
"scales": [
{
"name": "color",
"type": "linear",
"domain": [90, 190],
"range": {"scheme": "blueorange"}
}
],
"marks": [
{
"type": "path",
"from": {"data": "contours"},
"encode": {
"enter": {
"stroke": {"value": "#ccc"},
"strokeWidth": {"value": 1},
"fill": {"scale": "color", "field": "contour.value"}
}
},
"transform": [
{
"type": "geopath",
"field": "datum.contour"
}
]
}
]
}